There is an increasing interest in 3D X-ray imaging to move towards quantitative imaging. One route that is pursued is the use of dual energy (or even energy resolving) acquisition schemes in order to provide quantitative, monochromatic images.
U.S. Pat. No. 4,029,963 A discloses projection measurements made of the transmitted x-ray beam in low and high energy regions. Such projection measurements are combined in a non-linear processor to produce atomic-number-dependent and density-dependent projection information. This information is used to provide cross-sectional images which are free of spectral-shift artifacts and completely define the specific material properties. WO 2009/113713 A1 discloses a computing unit that computationally determines a quantity of an X-ray phase attributable to the object of examination and an X-ray transmittance of the object of examination from data detected by the detector. WO 2011/145040 A1 relates to an image processing apparatus for filtering an image. Said apparatus comprises an image input for obtaining a first and a second image of the same object, the first and second images comprising a plurality of voxels and being interrelated by a noise covariance, each voxel having a voxel value including a signal value and a noise value. EP 2 437 051 A1 discloses pseudo dual-energy material identification systems and methods with under-sampling.